1、Designation: D8027 16D8027 17Standard Practice forConcentration of Select Radionuclides Using MnO2 forMeasurement Purposes1This standard is issued under the fixed designation D8027; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, t
2、he year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice is intended to provide a variety of approaches in which manganese oxide (MnO2) can be used to
3、 concentrateradionuclides of interest into a smaller volume counting geometry or exclude other species that would otherwise impedesubsequent chemical separation steps in an overall radiochemical method, or both.1.2 The values stated in SI units are to be regarded as standard. No other units of measu
4、rement are included in this standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimit
5、ations prior to use.1.4 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Tech
6、nical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD7902 Terminology for Radiochemical Analyses3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this standard, refer to Terminologies D1129 and D7902.4. Summary of P
7、ractice4.1 These practices describe different processes through which MnO2 can be used to concentrate specific radionuclides ofinterest into a smaller volume counting geometry or exclude other species that would otherwise impede subsequent chemicalseparation steps in an overall radiochemical method,
8、 or both.4.2 Published studies (1-5)3 have addressed in detail the various manners in which hydrous manganese dioxides can besynthesized and the variety of crystal forms of hydrous manganese dioxide that can result. The literature describes the followinggeneral categories in which hydrous manganese
9、dioxide can be prepared.4.2.1 Guyard Reaction:3Mn2112MnO412H2O5MnO214H14.2.2 By the reduction of permanganate with reducing reagents such as hydrogen peroxide (H2O2) or hydrogen chloride (HCl).4.2.3 By the oxidation of Mn(II) salt under alkaline conditions with oxidizing reagents such as potassium c
10、hlorate (KClO3),H2O2, ozone (O3), or ammonium persulfate (NH4)2S2O8).4.3 The presented practices are not meant to address every possible approach to the generation and use of MnO2 but are meantto present some more typical practices that may be generally useful.1 This practice is under the jurisdicti
11、on ofASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.04 on Methods of RadiochemicalAnalysis.Current edition approved Feb. 15, 2016June 1, 2017. Published May 2016June 2017. Originally approved in 2016. Last previous edition approved in 2016 as D8027 16. DOI: 10.1520/
12、D8027-16.10.1520/D8027-17.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 The boldface numbers in parenthes
13、es refer to a list of references at the end of this standard.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all cha
14、nges accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. U
15、nited States15. Significance and Use5.1 This practice is applicable to the separation of specific radionuclides of interest as part of overall radiochemical analyticalmethods. Radionuclides of interest may need to be quantified at activity levels of less than 1 Bq. This may require measurementof les
16、s than 1 fg of analyte in a sample which has a mass of a gram to more than several kilograms. This requires concentrationof radionuclides into a smaller volume counting geometry or exclusion of species which would impede subsequent chemicalseparations, or both. MnO2 has shown good selectivity in bei
17、ng able to concentrate the following elements: actinium (Ac), bismuth(Bi), lead (Pb), polonium (Po), plutonium (Pu), radium (Ra), thorium (Th), and uranium (U) as noted in the referenced literature(see Sections 4 and 8).The MnO2 can be loaded onto a variety of substrates in preparation for use or ge
18、nerated in-situ in an aqueoussolution. The presented processes are not meant to be all encompassing of what is possible or meant to address all limitations ofusing MnO2. Some limitations are noted in Section 6, Interferences.6. Interferences6.1 MnO2 is able to achieve a very good decontamination fac
19、tor from monovalent cations in solution as evidenced by 8.38.5below in which it is used in seawater. However, in the case of elevated concentrations of divalent cations, for example barium,the recovery of analytes of interest can be significantly reduced (6). Additionally in the case of seawater, th
20、e recovery of analytessuch as uranium may also be substantially reduced. In such cases the use of an isotopic tracer can be very important to correct forsuch reduced recovery.The MnO2 separation is also very conducive to being easily repeated to achieve a second stage of separationfrom potentially i
21、nterfering species.7. ReagensReagents7.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that allreagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, wheresuch specifica
22、tions are available.4 Other grades may be used, provided that the reagent is of sufficiently high purity to permit itsuse without increasing the background of the measurement.7.1.1 Some reagents, even those of high purity, may contain naturally occurring radioactivity, such as isotopes of uranium,ra
23、dium, actinium, thorium, rare earths and potassium compounds or artificially produced radionuclides, or both. Consequently,when such reagents are used in the analysis of low-radioactivity samples, the activity of the reagents shall be determined underanalytical conditions that are identical to those
24、 used for the sample. The activity contributed by the reagents may be consideredto be a component of background and applied as a correction when calculating the test sample result. This increased backgroundreduces the sensitivity of the measurement.7.2 Ammonium hydroxide, 15 M NH4OH, (concentrated r
25、eagent).7.3 Ammonium hydroxide, 6 M NH4OHAdd 400 mL of concentrated ammonium hydroxide to 400 mL water. Dilute to 1 Lwith water and mix well.7.4 Bromocresol purple pH indicatorAdd 0.1 g bromocresol purple in 18.5 mLof 0.01 M sodium hydroxide (NaOH) solution.Dilute to 250 mL with water and mix well.7
26、.5 Hydrogen peroxide, 30 % H2O2. The ACS specification allows for a concentration range of 29 to 32 %.7.6 Iron chloride, FeCl3.7.7 Potassium permanganate, KMnO4.7.8 Potassium permanganate, 0.5 M KMnO4Add 79 g of KMnO4 to 750 mL water. Dilute to 1 L with water and mix well.7.9 Sodium hydroxide, 0.01
27、M NaOHAdd 0.1 g NaOH to 250 mL water.7.10 Phenolphthalein pH indicator solutionCommercially available as 1 % solution in ethanol.7.11 Sodium hydroxide, 10 MCarefully dissolve 400 g of NaOH in about 900 mL of water and dilute to 1 L.7.12 Manganese (II) chloride, 0.5 MDissolve 11.7 g of MnCl26H2O in a
28、bout 80 mL of water and dilute to 100 mL.8. Procedure8.1 Use of MnO2 Generated in-situ to Pre-Concentrate Sample Analytes:8.1.1 The precipitation of MnO2 from a water sample may be most conveniently performed on a volume of 0.1 to 2 L but largervolumes are possible (7 and 8). Any isotopic tracers sh
29、ould be added and the valence states of the tracers and analyte speciesallowed to equilibrate before proceeding.4 Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, DC. For suggestions on the testing of reagents not listed bythe American Chemical Soci
30、ety, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and NationalFormulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.D8027 1728.1.2 Add to the water sample approximately 10 mg of KMnO4 and allow to dissolve. Optionally
31、, approximately 2 mg of FeCl3may also be added to improve the obtainable separation factor.8.1.3 The pH indicator bromocresol purple may be added to the water sample to provide a color indicator in the following stepof raising the pH.8.1.4 Add to the water sample approximately 1 mL of about 30 % H2O
32、2.8.1.5 The precipitation step to follow is best performed at ambient temperature if a period of one or more days is available toallow for complete settling and development of the precipitate. Alternatively the promptness of the precipitation can be assistedby gently heating the water sample, for ex
33、ample to approximately 7080C.8.1.6 Add sufficient 6 M NH4OH to the water sample to raise the pH to about 8. If bromocresol purple was added in the priorstep this pH would be indicated by a color change to purple. The needed pH change could also be measured through use of pHtest strip or pH meter.8.1
34、.7 Following complete development and settling of the precipitate the supernate may be removed by aspiration or carefuldecantation. The small amount of MnO2 precipitate may be optimally isolated into a small pellet by transferring the bottom layercontaining the precipitate (about 50 mL) to a centrif
35、uge tube and centrifuging. The precipitate may be further washed up to twotimes with water and centrifugation repeated.8.1.8 An alternative to centrifugation is filtration through a 0.45 m filter but may require more time to accomplish the filtrationin a careful manner.NOTE 1A similar procedure can
36、be used on acid leachates of sediment samples but care should be taken when adding 6 M NH4OH to strong acidsolutions.8.1.9 The washed MnO2 precipitate and the incorporated analytes of interest and associated isotopic tracers may be takenthrough further separative steps, for example extraction chroma
37、tography, or may be transferred to a suitable counting geometry.8.2 In-situ MnO2 Precipiation by Oxidation of Mn(II) using H2O2:8.2.1 An example of forming an in-situ MnO2 precipitate by oxidation of Mn(II) salt using H2O2 is given in this section. Thisexample has been used to pre-concentrate radium
38、 from 0.5 L aqueous samples for the determination of 224Ra and 226Ra by alphaspectrometry.8.2.2 Add an appropriate amount of 225Ra tracer to the sample aliquant.8.2.3 Acidify the sample using nitric or hydrochloric acid. An approximate acid concentration of 0.1 to 0.2 M is suggested.8.2.4 Adjust the
39、 pH of the sample using phenolphthalein pH indicator and 10 M NaOH to produce the first sustained pink colorand then add a few additional drops of 10 M NaOH to provide a basic solution with a pH between 10 and 12. Perform the pHadjustment and the following steps while continuously stirring on a stir
40、 plate with a magnetic stir bar.8.2.5 Add 1 mL of 0.5 M Manganese (II) chloride and mix well.8.2.6 Add approximately 2 mL of 30 % H2O2 using a plastic transfer pipette.8.2.7 MnO2 precipitate (blackish color) will rapidly form and effervescence occurs.8.2.8 Continue stirring until effervescence subsi
41、des and then allow the precipitate to settle (remove the magnetic stir bar).8.2.9 Most of the supernatant is removed by aspiration or decantation after the precipitate has settled. Transfer the remainingsuspension to a centrifuge tube and isolate the MnO2 precipitate by centrifuging and decanting th
42、e supernatant. Alternatively if amore rapid analysis is required the MnO2 may be isolated immediately after precipitation is complete by centrifuging in a largevolume centrifuge bottle (this eliminates the time required for settling).8.2.10 It may be advantageous to reduce the amount of calcium reta
43、ined by the MnO2 precipitate. For example thedetermination of 224Ra and 226Ra by alpha spectrometry can be adversely affected by excessive calcium. If calcium levels are toohigh CaSO4 will precipitate during the Ba/RaSO4 microprecipitation step and spectral quality will be degraded. The followingste
44、ps describe an approach for reducing calcium retained on the MnO2 precipitate.8.2.10.1 Dissolve MnO2 precipitate which has been collected in a centrifuge tube with 5 mL of 2 M HCl and about 0.1 mL of30 % H2O2. Cap the tube and shake vigorously to facilitate dissolution.8.2.10.2 Dilute to about 40 mL
45、 and add about 0.1 mL of 30 % H2O2.8.2.10.3 Re-precipitate MnO2 by adding approximately 2 mL of concentrated NH4OH with a plastic transfer pipette. Cap tubeand mix gently. MnO2 precipitate will form and effervescence will occur. Loosen cap to vent gas. Tighten cap and gently mixseveral times over a
46、period of several minutes until the precipitate settles and a clear supernatant appears.8.2.10.4 Centrifuge the suspension and decant the supernatant. The supernatant will contain a significant fraction of the calciumwhich was retained on the original MnO2 precipitate (thus reducing the amount of ca
47、lcium retained by the MnO2).8.2.10.5 The MnO2 re-precipitation described above can be repeated if necessary to further reduce calcium retained on theMnO2 precipitate.8.3 Screening for Naturally Occurring Radionuclides using MnO2:8.3.1 MnO2 freshly precipitated from aqueous samples effectively retain
48、s a variety of naturally occurring radionuclides such asradium, thorium, uranium, polonium, actinium, and lead. Sodium and calcium are much more weakly retained. Freshly precipitatedMnO2 could provide a useful approach for screening for naturally occurring alpha and beta emitters in samples with hig
49、h levelsof sodium and calcium. Larger volumes could be analyzed since most of the sodium and calcium are not retained and the massD8027 173of the MnO2 precipitate is much less than the mass of salts obtained by evaporation. Useful techniques for preparing a countingsource from a MnO2 precipitate could include:8.3.1.1 Direct collection by filtration.8.3.1.2 Dissolution with nitric acid and H2O2 followed by evaporation on a stainless steel planchet.8.3.1.3 Dissolution with dilute acid and H2O2 and then mixing with liquid scintillation cocktail.8.4 Use of MnO2 Impreg
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